Source: node.go in package github.com/russross/blackfriday/v2

package blackfriday

import (
	"bytes"
	"fmt"
)

NodeType specifies a type of a single node of a syntax tree. Usually one node (and its type) corresponds to a single markdown feature, e.g. emphasis or code block.

type NodeType int

Constants for identifying different types of nodes. See NodeType.

const (
	Document NodeType = iota
	BlockQuote
	List
	Item
	Paragraph
	Heading
	HorizontalRule
	Emph
	Strong
	Del
	Link
	Image
	Text
	HTMLBlock
	CodeBlock
	Softbreak
	Hardbreak
	Code
	HTMLSpan
	Table
	TableCell
	TableHead
	TableBody
	TableRow
)

var nodeTypeNames = []string{
	Document:       "Document",
	BlockQuote:     "BlockQuote",
	List:           "List",
	Item:           "Item",
	Paragraph:      "Paragraph",
	Heading:        "Heading",
	HorizontalRule: "HorizontalRule",
	Emph:           "Emph",
	Strong:         "Strong",
	Del:            "Del",
	Link:           "Link",
	Image:          "Image",
	Text:           "Text",
	HTMLBlock:      "HTMLBlock",
	CodeBlock:      "CodeBlock",
	Softbreak:      "Softbreak",
	Hardbreak:      "Hardbreak",
	Code:           "Code",
	HTMLSpan:       "HTMLSpan",
	Table:          "Table",
	TableCell:      "TableCell",
	TableHead:      "TableHead",
	TableBody:      "TableBody",
	TableRow:       "TableRow",
}

func (t NodeType) String() string {
	return nodeTypeNames[t]
}

ListData contains fields relevant to a List and Item node type.

type ListData struct {
	ListFlags       ListType
	Tight           bool   // Skip <p>s around list item data if true
	BulletChar      byte   // '*', '+' or '-' in bullet lists
	Delimiter       byte   // '.' or ')' after the number in ordered lists
	RefLink         []byte // If not nil, turns this list item into a footnote item and triggers different rendering
	IsFootnotesList bool   // This is a list of footnotes
}

LinkData contains fields relevant to a Link node type.

type LinkData struct {
	Destination []byte // Destination is what goes into a href
	Title       []byte // Title is the tooltip thing that goes in a title attribute
	NoteID      int    // NoteID contains a serial number of a footnote, zero if it's not a footnote
	Footnote    *Node  // If it's a footnote, this is a direct link to the footnote Node. Otherwise nil.
}

CodeBlockData contains fields relevant to a CodeBlock node type.

type CodeBlockData struct {
	IsFenced    bool   // Specifies whether it's a fenced code block or an indented one
	Info        []byte // This holds the info string
	FenceChar   byte
	FenceLength int
	FenceOffset int
}

TableCellData contains fields relevant to a TableCell node type.

type TableCellData struct {
	IsHeader bool           // This tells if it's under the header row
	Align    CellAlignFlags // This holds the value for align attribute
}

HeadingData contains fields relevant to a Heading node type.

type HeadingData struct {
	Level        int    // This holds the heading level number
	HeadingID    string // This might hold heading ID, if present
	IsTitleblock bool   // Specifies whether it's a title block
}

Node is a single element in the abstract syntax tree of the parsed document. It holds connections to the structurally neighboring nodes and, for certain types of nodes, additional information that might be needed when rendering.

type Node struct {
	Type       NodeType // Determines the type of the node
	Parent     *Node    // Points to the parent
	FirstChild *Node    // Points to the first child, if any
	LastChild  *Node    // Points to the last child, if any
	Prev       *Node    // Previous sibling; nil if it's the first child
	Next       *Node    // Next sibling; nil if it's the last child

	Literal []byte // Text contents of the leaf nodes

	HeadingData   // Populated if Type is Heading
	ListData      // Populated if Type is List
	CodeBlockData // Populated if Type is CodeBlock
	LinkData      // Populated if Type is Link
	TableCellData // Populated if Type is TableCell

	content []byte // Markdown content of the block nodes
	open    bool   // Specifies an open block node that has not been finished to process yet
}

NewNode allocates a node of a specified type.

func NewNode(typ NodeType) *Node {
	return &Node{
		Type: typ,
		open: true,
	}
}

func (n *Node) String() string {
	ellipsis := ""
	snippet := n.Literal
	if len(snippet) > 16 {
		snippet = snippet[:16]
		ellipsis = "..."
	}
	return fmt.Sprintf("%s: '%s%s'", n.Type, snippet, ellipsis)
}

Unlink removes node 'n' from the tree. It panics if the node is nil.

func (n *Node) Unlink() {
	if n.Prev != nil {
		n.Prev.Next = n.Next
	} else if n.Parent != nil {
		n.Parent.FirstChild = n.Next
	}
	if n.Next != nil {
		n.Next.Prev = n.Prev
	} else if n.Parent != nil {
		n.Parent.LastChild = n.Prev
	}
	n.Parent = nil
	n.Next = nil
	n.Prev = nil
}

AppendChild adds a node 'child' as a child of 'n'. It panics if either node is nil.

func (n *Node) AppendChild(child *Node) {
	child.Unlink()
	child.Parent = n
	if n.LastChild != nil {
		n.LastChild.Next = child
		child.Prev = n.LastChild
		n.LastChild = child
	} else {
		n.FirstChild = child
		n.LastChild = child
	}
}

InsertBefore inserts 'sibling' immediately before 'n'. It panics if either node is nil.

func (n *Node) InsertBefore(sibling *Node) {
	sibling.Unlink()
	sibling.Prev = n.Prev
	if sibling.Prev != nil {
		sibling.Prev.Next = sibling
	}
	sibling.Next = n
	n.Prev = sibling
	sibling.Parent = n.Parent
	if sibling.Prev == nil {
		sibling.Parent.FirstChild = sibling
	}
}

func (n *Node) isContainer() bool {
	switch n.Type {
	case Document:
		fallthrough
	case BlockQuote:
		fallthrough
	case List:
		fallthrough
	case Item:
		fallthrough
	case Paragraph:
		fallthrough
	case Heading:
		fallthrough
	case Emph:
		fallthrough
	case Strong:
		fallthrough
	case Del:
		fallthrough
	case Link:
		fallthrough
	case Image:
		fallthrough
	case Table:
		fallthrough
	case TableHead:
		fallthrough
	case TableBody:
		fallthrough
	case TableRow:
		fallthrough
	case TableCell:
		return true
	default:
		return false
	}
}

func (n *Node) canContain(t NodeType) bool {
	if n.Type == List {
		return t == Item
	}
	if n.Type == Document || n.Type == BlockQuote || n.Type == Item {
		return t != Item
	}
	if n.Type == Table {
		return t == TableHead || t == TableBody
	}
	if n.Type == TableHead || n.Type == TableBody {
		return t == TableRow
	}
	if n.Type == TableRow {
		return t == TableCell
	}
	return false
}

WalkStatus allows NodeVisitor to have some control over the tree traversal. It is returned from NodeVisitor and different values allow Node.Walk to decide which node to go to next.

type WalkStatus int

GoToNext is the default traversal of every node.

SkipChildren tells walker to skip all children of current node.

Terminate tells walker to terminate the traversal.

	Terminate
)

NodeVisitor is a callback to be called when traversing the syntax tree. Called twice for every node: once with entering=true when the branch is first visited, then with entering=false after all the children are done.

type NodeVisitor func(node *Node, entering bool) WalkStatus

Walk is a convenience method that instantiates a walker and starts a traversal of subtree rooted at n.

func (n *Node) Walk(visitor NodeVisitor) {
	w := newNodeWalker(n)
	for w.current != nil {
		status := visitor(w.current, w.entering)
		switch status {
		case GoToNext:
			w.next()
		case SkipChildren:
			w.entering = false
			w.next()
		case Terminate:
			return
		}
	}
}

type nodeWalker struct {
	current  *Node
	root     *Node
	entering bool
}

func newNodeWalker(root *Node) *nodeWalker {
	return &nodeWalker{
		current:  root,
		root:     root,
		entering: true,
	}
}

func (nw *nodeWalker) next() {
	if (!nw.current.isContainer() || !nw.entering) && nw.current == nw.root {
		nw.current = nil
		return
	}
	if nw.entering && nw.current.isContainer() {
		if nw.current.FirstChild != nil {
			nw.current = nw.current.FirstChild
			nw.entering = true
		} else {
			nw.entering = false
		}
	} else if nw.current.Next == nil {
		nw.current = nw.current.Parent
		nw.entering = false
	} else {
		nw.current = nw.current.Next
		nw.entering = true
	}
}

func dump(ast *Node) {
	fmt.Println(dumpString(ast))
}

func dumpR(ast *Node, depth int) string {
	if ast == nil {
		return ""
	}
	indent := bytes.Repeat([]byte("\t"), depth)
	content := ast.Literal
	if content == nil {
		content = ast.content
	}
	result := fmt.Sprintf("%s%s(%q)\n", indent, ast.Type, content)
	for n := ast.FirstChild; n != nil; n = n.Next {
		result += dumpR(n, depth+1)
	}
	return result
}

func dumpString(ast *Node) string {
	return dumpR(ast, 0)